Conventionally, known methods for producing optically active alcohol compounds have involved the catalytic asymmetric reduction of carbonyl compounds such as ketones. Examples of these known methods include methods using a rhodium complex disclosed in Non-Patent Documents 1 and 2, a method using an iridium complex disclosed in Non-Patent Document 3, a method disclosed in Patent Document 1 that involves performing a hydrogen transfer using ruthenium as a catalyst, and a method disclosed in Patent Document 2 that involves performing a hydrogenation using ruthenium as a catalyst.
However, of these methods, in the methods disclosed in Non-Patent Documents 1 to 3, the metal used as a catalyst is a comparatively expensive so-called noble metal such as rhodium or iridium, which also has a comparatively low hydrogenation activity, and when such a metal is used as an asymmetric reduction catalyst, a comparatively high temperature or high hydrogen pressure is required. In the method disclosed in Patent Document 1, an organic compound such as formic acid must be used as the hydrogen source, and therefore the method is unfavorable from an operational and cost perspective when compared with methods where a cheap hydrogen source such as hydrogen gas can be used. Further, although the method disclosed in Patent Document 2 is a superior asymmetric reduction method for carbonyl compounds, it also suffers from problems, including the fact that favorable results cannot be obtained without using a catalyst having an expensive bidentate phosphine ligand with a plurality of substituents, and a diamine ligand that is difficult to synthesize.
Accordingly, there has been considerable demand for the development of an inexpensive asymmetric hydrogenation catalyst which is capable of using an inexpensive hydrogen source such as hydrogen gas to convert a carbonyl compound to a corresponding optically active alcohol compound with high selectivity and high yield.
A multitude of ruthenium catalysts have already been developed, and of these, representative examples of several ruthenium catalysts having a phosphine ligand, which are the most similar to the present invention, are presented below.
(1) A ruthenium complex represented by formula (1):[Chemical formula 1]RuXY(PR1R2R3)n(NR6R7R8)m  (1)wherein X and Y may be the same or different, and each represents a hydrogen atom, halogen atom, carboxyl group or other anion group, R1, R2 and R3 may be the same or different, and each represents a hydrocarbon group that may have a substituent, or alternatively, R1 and R2 may be bonded together to form a carbon chain ring that may have a substituent, n represents an integer of 0 to 4, R6, R7 and R8 may be the same or different, and each represents a hydrogen atom or a hydrocarbon group that may have a substituent, and m represents an integer of 0 to 4 (see Patent Document 2).(2) a ruthenium compound represented by formula (2):[Chemical formula 2]Ru(X)(Y)(Px)n1[R1R2C*(NR3R4)-A-R5R6C*(NR7R8)]  (2)wherein each of X and Y independently represents a hydrogen atom, halogen atom, carboxyl group, hydroxyl group or C1 to C20 alkoxy group, Px represents a phosphine ligand, each of R1 to R8 independently represents a hydrogen atom, C1 to C20 alkyl group that may have a substituent, C2 to C20 alkenyl group that may have a substituent, C3 to C8 cycloalkyl group that may have a substituent, aralkyl group that may have a substituent, or aryl group that may have a substituent, and either of R1 and R2 may be bonded to either of R3 and R4 to form a ring, either of R5 and R6 may be bonded to either of R7 and R8 to form a ring, A represents a C1 to C3 alkylene that may have a substituent and may have an ether linkage, C3 to C8 cycloalkylene that may have a substituent, allylene that may have a substituent, or divalent hetero ring that may have a substituent, and in those cases where A represents an alkylene group, either of R1 and R2 may be bonded to either of R5 and R6 to form a ring, * indicates an asymmetric carbon atom, and n1 represents an integer of 1 or 2 (see Patent Document 3).(3) A ruthenium compound represented by formula (3):[Chemical formula 3]Ru(X)(Y)(Px)n(A)  (3)wherein each of X and Y independently represents a hydrogen atom, halogen atom, carboxyl group, hydroxyl group or C1 to C20 alkoxy group,Px represents a phosphine ligand, n represents 1 or 2, andA represents a diamine ligand represented by formula (4) or formula (5) shown below:[Chemical formula 4]R1CH(NH2)CH2(NR2R3)  (4)R1CH(NR2R3)CH2(NH2)  (5)
wherein R1 represents a C1 to C20 alkyl group that may have a substituent, C2 to C20 alkenyl group that may have a substituent, C3 to C8 cycloalkyl group that may have a substituent, C7 to C20 aralkyl group that may have a substituent, aryl group that may have a substituent, or heterocyclic group, each of R2 and R3 independently represents a hydrogen atom, C1 to C20 alkyl group that may have a substituent, C2 to C20 alkenyl group that may have a substituent, C3 to C8 cycloalkyl group that may have a substituent, or C7 to C20 aralkyl group that may have a substituent, and R2 and R3 may be bonded together to form a ring, provided that R2 and R3 are not both hydrogen atoms (see Patent Document 4).